Implementing Hazard Control Measures for Arc Hazard Protection

Although the electric arc flash hazard only recently has garnered the attention equal to that of the long-recognized hazard of electric shock, the arc hazard is not new. Until the 1980s, occupational electrical hazards generally were described in terms of electric shock or electrocution, a fatal electric shock.

Electric shock entails passage of an electric current through the body. A shock victim generally must make contact with an energized conductor, or otherwise become part of the electrical circuit. Arc flash victims do not have to make physical contact with an energized conductor or be a part of the electrical circuit. The victim may be several feet away from energized conductors or equipment and be severely injured by the intense thermal energy transfer produced by an electric arc. The burn injuries can be radiant burns to bare exposed skin, large-area body burns from ignition or melting of clothing or burns caused by heat transfer through clothing, including flame-resistant clothing.

ABOUT ARC FLASH

Arc flash events usually are very short occurrences — typically less than 0.5 seconds in duration. They can be initiated by a wide range of factors and complicated by other contributing factors. There can be human errors, such as touching an energized conductor the employee thought was de-energized, or accidentally dropping a tool onto an energized conductor.

In addition, there may be environmental causes, such as roof leaks or dirt accumulation in electrical switchgear. There may be management system failures in critical aspects of training, maintenance programs, design specifications or tool requirements, such as allowing use of voltage testing devices not rated for industrial and commercial electrical systems. Switchgear or other equipment failures during switching or operating interaction also can expose workers to the hazards of electric arc flash.

Most arc flash events occur faster than the unaided human eye can perceive. High-speed photography of laboratory simulations of arcing faults have provided images of how these events can engulf workers in a ball of fire. Electric arcs are very hot; next to the laser, arc flashes create the most intense heat source on earth. Temperatures in the arc can reach 35,000 degrees F. Arc flash events actually are multiple energy events, with intense blast, mechanical and acoustic energy accompanying the intense thermal energy. People within several feet of an arc can be severely burned.

As the body of knowledge and understanding of the arc flash phenomena grew, leadership emerged to change federal regulations; update building codes; improve the design of electrical equipment; increase the application of circuit protection; create safe work practices; train personnel in utility, industrial and commercial work environments; and develop personal protective equipment (PPE). Technologies to further reduce or mitigate arc flash hazards were brought to market, including current limitation, metal cladding, venting to redirect arc blast forces and “arc resistant” designs.

In 2004, the National Fire Protection Association (NFPA) and the Institute of Electrical and Electronics Engineers Inc. (IEEE) established a collaborative research project to further study the phenomena of electric arcs. This collaboration helped advance the protection of workers from heat, pressure, sound, toxicity and other medical effects of exposure to electric arcs.

HAZARD CONTROL MEASURES

Below are a few examples of applying hazard control measures to the unique hazard of electric arc flash. The examples are not all-inclusive, and only serve to illustrate concepts useful in helping assure long-term effectiveness and sustainability. The most effective design and application of an arc flash mitigation program incorporating these control measures usually can best be achieved through a collaboration involving electrical subject matter experts, safety professionals knowledgeable in safety management systems and management resources that can help assure financial and other resources are allocated to the program.

Electrical experts may be knowledgeable in all things electrical, but not in the subtleties of safety management systems. Safety professionals, on the other hand, may be expert in safety management, but have only a general or limited knowledge of electrical equipment and work practices. Bringing experts from different competencies together can produce high quality results in fleshing out details of an effective and sustainable electrical safety program.

Eliminating the hazard — With a high degree of certainty, the best way to protect people from an arc flash exposure is to completely eliminate the arc hazard. It is easier to design new facilities with the intent to eliminate arc flash hazards than it is to retrofit existing electrical installations.

However, an organization that asks the question, “Do we have any exposures that are unnecessary and could be eliminated?” may discover some opportunities. One example is the discovery that a long-established employee break area, located in an electrical control room, was within the calculated arc flash boundary. While the individuals in the break area may not have interacted directly with the electrical equipment, the routine congregation of people within the arc flash boundary created an unnecessary risk. Relocating the break area to a new location eliminated the hazard.